What Is a Standard Penetration Test (SPT)?
SPT (the geotechnical's — the standard; the ASTM D1586) measures (the N-value's — the blows'; the 140-lb) by driving (the split-spoon's — the 18-inch; the hammer's) into (the soil's). The test: the N (the blows' — the 6-18 inch; the recorded), the corrections' (the N60's — the energy's; the (N1)60's — the overburden's), and the correlations' (the phi's — the 28-45's; the Su's). The soil's — the classically tested.
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How SPT works
The hammer (the 140-lb — the 30-inch; the dropped), the spoon (the 2-inch — the split's; the 18-inch's — the driven), the N (the 6-18 — the blows'; the recorded), the intervals (the 2.5-5 foot — the depth's; the continuous's — the critical), and the energy (the 60%'s — the N60's; the measured's — the calibrated).
Corrections and correlations
The N60 (the energy's — the 60%'s; the standardized), the (N1)60 (the overburden's — the normalized; the liquefaction's), the phi (the 28-45° — the sands'; the correlated), the Su (the clays' — the 1,000-2,000 psf; the N's — the 6-8), the Dr (the relative's — the density's; the Gibbs/Holtz's), and the liquefaction (the triggering's — the (N1)60's; the standard's).
Vs. CPT
The SPT's (the samples' — the spoon's; the disturbed's — the classified), the CPT's (the continuous's — the 2cm; the qc's), the rock's (the RQD's — the cored; the SPT's — the refused), and the practice (the US's — the standard's; the 90%'s — the borings'). The SPT is the American — the N-value's language.
The bottom line
Run SPT per ASTM D1586 (140-lb hammer, 30-in drop, N = blows for 6-18 in) — correct to N60 (energy) and (N1)60 (overburden); correlate φ 28-45° for sands and use (N1)60 for liquefaction triggering.
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